This invention relates to a device for driving an EC (electrochromic) antiglare mirror used as an inside or outside rear view mirror.
An EC antiglare mirror is made by covering the front surface of the reflecting surface of a mirror with an EC element film and achieves an antiglare effect against light from headlights of a succeeding vehicle while running at night by changing the amount of coloration of the EC element and thereby controlling reflectivity of the mirror. For obtaining such antiglare effect, the antiglare mirror is so controlled that, upon detection of quantity of incident light from the rear, the amount of coloration increases (i.e., reflectivity decreases) when the light from the rear is strong whereas the amount of coloration decreases ( the color fades, i.e., reflectivity increases) when the light from the rear is weak.
The glare of the light to the human eye, however, is produced by entire surrounding light and, therefore, the control based on the light from the rear only does not match the human sense. For this reason, a control is generally made in such a manner that not only rear light but also surrounding light is detected and color imparting and color fading controls are made in accordance with quantity of the detected rear and surrounding light. More specifically, when surrounding light is strong, the glare of the light is not so strong notwithstanding that there is rear light. In this case, the sensitivity of detection for the rear light is reduced for making it harder for the EC element to be colored. When the surrounding light is weak, the glare of the light to the rear light is strong and, in this case, sensitivity of detection for the rear light is raised for making it easier for the EC element to be colored. In the prior art EC antiglare mirror, surrounding light and rear light are detected and a value of voltage applied to the EC element is obtained in accordance with a combination of the surrounding light and the rear light and the amount of coloration, i.e., reflectivity, is controlled by this voltage.
This prior art method, however, requires a structure for combining detected values of the surrounding light and the rear light and obtaining a control amount of a single object of control.
It is an object of the invention to provide a device for driving an EC antiglare mirror which has overcome the above described problem of the prior art method and enables control of the amount of coloration by controlling the surrounding light and the rear light individually as separate objects of control and thereby realizes a simplified structure of the device.